#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int fun(int n)
{
    if (n == 1)
        return 1;
    else if (n == 2)
        return 2;
    else
        return fun(n - 1) + fun(n - 2);
}
int main()
{
    int n = 0;
    int w = 0;
    scanf("%d", &n);
    w = fun(n);
    printf("%d\n", w);
    return 0;
}